1. Field of the Invention
The present invention relates to a method of driving a liquid crystal panel, which is preferably used in driving of an active matrix liquid crystal panel for achieving excellent display quality at ambient temperature in a range of low temperature to high temperature.
2. Description of the Background Art
In writing to pixels of a typical liquid crystal display device using an active matrix liquid crystal panel, a waveform becomes blunt due to interconnection resistance in a gate selection signal as well as an image data signal. For this reason, as commonly known in Japanese Patent Application Laid-Open No. 59-123884, signal timings thereof are set by being shifted somewhat form each other. Specifically, driving is performed such that a gate selection signal goes high to input an image data signal and then the gate selection signal goes low to end the image data signal. However, an influence of a waveform becoming blunt differs between pixels close to external input units of respective signals in a display area and pixels far therefrom, and thus timing is set so as not to incur a problem in an entire display area due to writing timing. A charging time of a pixel ranges from a rise of the image data signal to a fall of the gate selection signal.
Horizontal scanning interconnections and data interconnections of a liquid crystal panel are typically formed of metal interconnection. Thus, in a case where a liquid crystal display device is used in a wide temperature range from low temperature to high temperature, interconnection resistance becomes high at high temperature to increase an RC time constant, which increases a signal delay as well. As a result, signal waveforms of the horizontal scanning interconnections become blunt, which causes a failure in writing timing.
Although it is possible to take measures against this by adjusting timings in consideration of a signal delay due to a waveform becoming blunt at high temperature as descried in Japanese Patent Application Laid-Open No. 59-123884 (in particular, FIG. 3), unfortunately, this method reduces a charging time. A thin film transistor (hereinafter, referred to as TFT) which drives a pixel is formed of a semiconductor (amorphous Si). An on-current thereof decreases at low temperature, and thus a pixel is insufficiently charged, which leads to display unevenness. It is effective to increase a charging time for improving display at low temperature, which is difficult to be compatible with the measure against a signal delay at high temperature.